rename: prefix gateway projects/namespaces with ZB.MOM.WW + sln→slnx

Apply the ZB.MOM.WW. prefix to all gateway-side projects, folders,
.csproj/.sln contents, C# namespaces, using directives, generated proto
C# (csharp_namespace + checked-in generated files), InternalsVisibleTo
attributes, project-name string literals (LoadProject, .sln lookups,
worker exe paths, staticwebassets manifest), and the install/script/doc
references that point at any of the above. Migrate the solution from
.sln to .slnx via `dotnet sln migrate` and delete the old file.

External-runtime identifiers are intentionally NOT prefixed so external
configuration keeps working:
- GatewayMetrics.cs MeterName ("MxGateway.Server")
- DashboardAuthenticationDefaults Scheme/Policy ("MxGateway.Dashboard")
- GatewayRequestLoggingMiddleware logger category ("MxGateway.Request")
- StaRuntime thread name ("MxGateway.Worker.STA")
- appsettings.json root section "MxGateway" + env-var prefix
  MxGateway__... and secret-name MxGateway:ApiKeyPepper
- C:\ProgramData\MxGateway\ data dir paths

Also fixes two tests that were not rename-related but became visible
while validating the rename:

- WorkerLiveMxAccessSmokeTests.ShutDownAsync: cancellation that the
  gateway service correctly maps to RpcException(Cancelled) per gRPC
  convention was being misclassified as a stream fault. Added a sibling
  catch on RpcException with StatusCode.Cancelled.

- IntegrationTestEnvironment.ResolveRepositoryRoot: extracted IsRepositoryRoot
  and made it accept either a .git marker OR a .sln/.slnx next to src/
  so the worker-exe walker works in non-git working copies.

clients/proto/proto-inputs.json's protoRoot updated to point at
src/ZB.MOM.WW.MxGateway.Contracts/Protos.

Verified by `dotnet build` and a full `dotnet test` of the .slnx with
MXGATEWAY_RUN_LIVE_{MXACCESS,LDAP,GALAXY}_TESTS=1:
  Tests: 472/472 pass
  Worker.Tests: 280/280 pass (4 dev-rig [Fact(Skip=...)] skipped)
  IntegrationTests: 18/18 pass

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/ImplementationPlanGateway.md

@@ -22,19 +22,19 @@ Labels: `area:gateway`, `type:infra`, `priority:p0`
 
 Deliverables:
 
-- create `src/MxGateway.sln`,
-- create `src/MxGateway.Contracts`,
-- create `src/MxGateway.Server`,
-- create `src/MxGateway.Tests`,
-- create `src/MxGateway.IntegrationTests`,
-- target `MxGateway.Server` to `net10.0`,
+- create `src/ZB.MOM.WW.MxGateway.slnx`,
+- create `src/ZB.MOM.WW.MxGateway.Contracts`,
+- create `src/ZB.MOM.WW.MxGateway.Server`,
+- create `src/ZB.MOM.WW.MxGateway.Tests`,
+- create `src/ZB.MOM.WW.MxGateway.IntegrationTests`,
+- target `ZB.MOM.WW.MxGateway.Server` to `net10.0`,
 - add shared C# build settings in `Directory.Build.props`,
 - add baseline tests.
 
 Acceptance criteria:
 
-- `dotnet build src/MxGateway.sln` succeeds,
-- `dotnet test src/MxGateway.sln` succeeds,
+- `dotnet build src/ZB.MOM.WW.MxGateway.slnx` succeeds,
+- `dotnet test src/ZB.MOM.WW.MxGateway.slnx` succeeds,
 - gateway project does not reference MXAccess COM.
 
 ### Issue: Define Protobuf Contracts
@@ -43,8 +43,8 @@ Labels: `area:contracts`, `type:feature`, `priority:p0`
 
 Deliverables:
 
-- `src/MxGateway.Contracts/Protos/mxaccess_gateway.proto`,
-- `src/MxGateway.Contracts/Protos/mxaccess_worker.proto`,
+- `src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto`,
+- `src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_worker.proto`,
 - `MxAccessGateway` service with `OpenSession`, `CloseSession`, `Invoke`, and
   `StreamEvents`,
 - `WorkerEnvelope` and worker IPC messages,